x11vnc: bump version to fix build issue with newer libX11

Fixes http://autobuild.buildroot.net/results/2733c2c9fa7aacb355e0e0b184a5afe41cf35a3d



Old x11vnc defined a 'pointer' function, which collides with the libX11
pointer type. Fix it by bumping the version (upstream renamed it to
pointer_event()).

Fix the dependencies and help text while we're at it.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>